Disentangling structural patterns of natural forest fragments in a savanna matrix in the eastern Brazilian Amazon

ABSTRACT Natural fragments are an important source of richness for the management and conservation of a local flora. The objective of this study was to evaluate the effect of fragmentation on the structure and composition of the plant communities of forest fragments (FF) in Alter do Chão, eastern Brazilian Amazonia. The study sample consisted of 25 FF and nine continuous forest (CF) sites. We compared plant density and species richness between site categories by t-tests, analyzed the differences in composition by cluster analysis, and assessed the effect of fragment size and distance to CF on the basal area and diameter of FF assemblages by linear regression. Individual trees and shrubs with DBH ≥1.27 cm were measured in 2x250 m plots. 17,078 individuals were recorded - 75.32% in FF and 24.68% in CF, comprising 475 species, 216 genera and 64 families. Myrtaceae and Fabaceae were the most abundant families in both FF and CF. Average species richness in FF and CF was statistically different. The 20 species with the highest importance values were similar in FF and CF. The average plant diameter was similar in FF and CF, suggesting that both are "mature" forests composed of thin individuals. Average diameter and total basal area showed a negative relationship with distance to CF and fragment area, respectively. Similarity analysis revealed two groups, one composed exclusively of portions of fragmented forest. Fragments and continuous forest differed in species composition, but were similar in structure. Diameter distribution in fragments was similar to that of primary forests

Alimentação e ecomorfologia de duas espécies de piranhas (Characiformes: Characidae) do lago de Viana, estado do Maranhão, Brasil Feeding and ecomorphology of two species of piranhas (Characiformes: Characidae) from the Viana Lake, Maranhão state, Brazil

Serrasalmus aff. brandtii e Pygocentrus nattereri são duas espécies de piranhas comuns no Lago de Viana, um lago formado a partir das inundações do Rio Pindaré, tributário da margem esquerda do Rio Mearim. Uma amostra composta por 249 exemplares destas espécies foi estudada a fim de identificar a composição da dieta e as estratégias alimentares empregadas pelas duas. Os peixes foram coletados trimestralmente durante um ano, entre março de 1998 e março de 1999, usando redes de emalhar e tarrafas. A composição qualitativa da dieta foi analisada com uso do método de freqüência de ocorrência. As estratégias alimentares empregadas pelas espécies foram inferidas através do método gráfico de Costello (1990), modificado por Amundsen et al. (1996). Os resultados indicaram que peixes foi o item encontrado com maior freqüência nos estômagos de ambas as espécies, seguido de matéria vegetal, com maior participação na dieta de P. nattereri. Os recursos peixes e vegetais tenderam a apresentar relações inversas quando comparados com as diferentes classes de comprimento. A análise gráfica da dieta de P. nattereri e S. aff. brandtii sugere que a maioria dos indivíduos utiliza vários recursos simultaneamente. Uma análise multivariada de índices ecomorfológicos indicou que as espécies são segregadas com relação à habilidade natatória, posição ocupada na coluna d'água e tamanho relativo das presas.<br>Serrasalmus aff. brandtii and Pygocentrus nattereri are two species of piranhas, both common in the Viana Lake, which is formed by the flooding waters of the Pindaré River, a tributary of the left bank of the Mearim River. A sample composed of 249 specimens of these species was studied in order to identify diet composition and feeding strategies employed by the two species. The piranhas were captured thrimonthly, during one year from March 1998 to March 1999 using gill and fishing nets of different mesh sizes. The qualitative composition of the diet was analysed through the frequency of occurrence method. The feeding strategies employed by the piranhas were inferred using the graphic method of Costello (1990), modified by Amundsen et al. (1996). The results indicated that fish was the main food item in the stomach contents of the two species, followed by plant material, more in the P. nattereri. Fish and plant material showed different relationships in relation to piranhas's length classes. The graphic analysis of the feeding strategies employed by P. nattereri and S. aff. brandtii suggest a generalist habit, wide width niche with strong participation of the within-phenotype component, which indicated that the majority of individuals of these species use several resources simultaneously. A multivariate analysis of the ecomorphological index indicated that the species are discriminated by swimming ability, water column position and relative prey size